Applicants herein have made the discovery that any type of focusing device in combination with a surface, exhibiting any degree of reflectivity and positioned near the focal plane of the device, acts as a retro-reflector. A retroreflector is defined as a reflector wherein incident rays or radiant energy and reflected rays are parallel for any angle of incidence within the field-of-view. A characteristic of a retroreflector is that the energy impinging thereon is reflected in a very narrow beam, herein referred to as the retroreflected beam. This phenomenon is termed retroreflection.
It is herein to be noted that the term radiant energy includes light energy, radio frequency, microwave energy, acoustical energy, X-ray energy, heat energy and any other types of energy which are part of the energy spectrum and which are capable of being retroreflected by the device, instrument or system sought to be detected.
One type of optical device which exhibits this phenomenon, and thus is a particular type of retroreflector, is a corner reflector consisting of three mutually perpendicular reflecting planes, However, this type of retroreflector is both difficult and expensive to fabricate.
Due to the applicants discovery, it has now become possible to accomplish a great many feats heretofore considered impossible, as will become more apparent from the discussion to follow hereinafter. In this context it should be noted that the eyes of human beings, as well as those of animals, operate as retroreflectors. Also, any optical instrument which includes a focusing lens and a surface having some degree of reflectivity, no matter how small, positioned near the focal point of the lens, act as a retroreflector, whereby any radiant energy from a radiant energy source directed at these instruments is reflected back towards the source in a substantially collimated narrow beam.
It is therefore the primary object of the present invention to provide a method and apparatus for detecting objects exhibiting retroreflection characteristics.
It is another object of the present invention to provide a method and apparatus to detect objects having retroreflection characteristics by illuminating the same with a radiant energy source.
It is a more particular object of the present invention to provide a method and apparatus for scanning an area to detect the presence of optical instruments such as binoculars, telescopes, periscopes, range finders, cameras, and the like.
It is a further object of the present invention to provide means and apparatus for determining the characteristics of a device exhibiting retroreflection characteristics from a remote location.
It is a further object of the present invention to provide a method and apparatus for detecting optical instruments for rendering the instruments ineffective and for neutralizing humans utilizing said instruments by employing lasers or similar high energy sources.
It is yet another object of the present invention to provide a method and apparatus for transmitting and receiving radiant energy utilizing concentric optics.